The structure, function and expression of the kertin intermediate filaments of human and mouse skin, and the related intermediate filament proteins of other cell types, are being investigated. These studies are designed to understand the structural features that determine how the rod domains of the chains pack to form the filament core. We have used cross-linking studies to determine molecular lengths and the nearest neighbor molecular alignments in the filaments. An assay involving synthetic peptides has been designed to explore the features of the filament models. The glycine-rich end domains of especially the keratin 1/10 filaments of epidermal cells are unique in biology. We believe these organize into a glycine-loop configuration. Current studies are designed to determine how these are packed and how they might interact with other macromolecules coexpressed in epidermal tissues. The glycine- loop sequences on the human keratin 10 chain are extraordinarily polymorphic in size and sequence. Using genomic clones to the human keratin chains 1 and 10, transgenic mice have been constructed to examine the expression characteristics of the genes as well as to probe in vivo the likely functions of the various portions of the chains, such as rod domain segments and glycine-rich end domains.